JP-A-2010-36834 (US 2010/0035534) describes an air-conditioner for a vehicle, and the air-conditioner has a two layer mode and an outside air mode. The air-conditioner has a first inlet introducing outside air and a second inlet introducing inside air. Further, an outside air passage and an inside air passage are independently defined in the air-conditioner.
When the two layer mode is selected, the first inlet and the second inlet are opened. The outside air and the inside air are simultaneously drawn into an air sending unit respectively from the first inlet and the second inlet, and flow in the outside air passage and the inside air passage respectively toward an air conditioning unit through a filter and a blower.
When the outside air mode is selected, only the first inlet is opened, and the outside air passage and the inside air passage are combined with each other. The outside air is drawn into the air sending unit from the first inlet, and flows toward the air conditioning unit through the whole surface of the filter and the blower.
While the outside air passes the filter, foreign matters such as dust or pollen are caught by the filter. However, at the two layer mode, because the outside air flows only a part of the filter adjacent to the first inlet, the foreign matters contained in the outside air adhere to the part of the filter adjacent to the first inlet.
When the two layer mode is switched into the outside air mode, the outside air flows through not only the part of the filter adjacent to the first inlet but also the other part of the filter adjacent to the second inlet. However, the pressure loss becomes higher in the part of the filter adjacent to the first inlet than the other part of the filter adjacent to the second inlet, so distribution of flow speed of the outside air becomes nonuniform over the filter. Further, because the clogging is accelerated in the part of the filter adjacent to the first inlet, it may be required to frequently replace the filter with a new filter.